1. Field of the Invention
The present invention relates to a position detector for a motor used for, e.g., a power window device that opens and closes a vehicle door window glass up and down or a sunroof device that opens and closes a sunroof door.
2. Description of Related Art
A motor is used as a driving source for a power window device that opens and closes a vehicle door window glass up and down or a sunroof device that opens and closes a sunroof door.
In power window devices, a catch prevention function is provided to prevent accidental catching of a passenger's body and/or foreign objects between a window glass and a window frame. Among such power window devices equipped with the catch prevention function, some devices have a limit switch provided at a specified position in the door. These types of devices determine whether or not any obstacle has been caught by the window glass based on a signal from the limit switch and a lock current of a motor, to control movement of the window glass, i.e., the rotation position of the motor. Other devices have a Hall IC or a special commutator for detecting rotation number of an armature and determine whether or not any obstacle has been caught based on a rotation speed detection signal (e.g., pulse number or width of pulse signals) to control the rotation position of the motor.
However, in those power window devices (i.e., motor rotation position detection mechanism), cumbersome adjustment of assembling position is required when the motor and a window regulator are assembled, and cumbersome resetting after assembling work is also required. Further, when the catch prevention mechanism is provided, other additional expensive parts such as a control device is required, but the accuracy is not greatly improved.
In view of the foregoing problems, the applicant proposed a position detector for a motor for a moving body in JP-A-8-29114 and JP-A-9-236431.
The proposed position detector for the moving body includes: a planetary gear train unit having a ring gear which is rotatably held in a cover plate and planetary gears engaged with the ring gear; a switch portion having a moving contact which is formed integrally with the ring gear to rotate with the ring gear and a fixed contact which is fixed on the cover plate to contact the moving contact; and a clutch mechanism which can shut off the transmission of the rotation force in the forward direction from the moving body (i.e., output shaft of the motor) to the ring gear. Thus, the position of the window glass or the sunroof door can be accurately detected and the movement thereof can be controlled when the position detector is applied to the power window device or the sunroof device. Further, the initial position can be set readily without cumbersome positional adjustment, and these effects can be realized by a simple mechanism at a low cost.
In the above-described position detector for the motor of the moving body, a pulse plate is connected to a sun gear (i.e., a motor output shaft of the moving body) of the planetary hear train unit and is rotated integrally with the sun gear to generate pulse signals. Therefore, the generated pulse signals can be detected, and the moving position of a moving body can be linearly detected according to the detected signals. Thus, the position of the window glass can be detected when the position detector is applied to the power window device.
However, in the position detector, only the outer periphery of the sun gear is fitted to the pulse plate so that the pulse plate is integrally rotated with the motor output shaft of the moving body. That is, a fitting hole having an octangular shape is formed at a center portion of the pulse plate, a shaft portion of the sun gear is formed in an octangular shape to correspond to the fitting hole, and the shaft portion of the sun gear is inserted into the fitting hole to integrally connect the sun gear and the pulse plate. Because the shaft portion of the sun gear is inserted into the fitting hole so that the pulse plate is connected to the sun gear, it is difficult to increase the connection strength between the pulse plate and the sun gear. Thus, when a rotational torque transmitted from the sun gear to the pulse plate becomes large, the connection between the sun gear and the pulse plate can be released so that only the sun gear may be idling.